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I think I’ve came across a contradiction in relation to these two phenomenon.

On the one hand there is the following example: there was a vintage advert against pollution whereby a lot of people were shown littering as an example of negative behaviour. This was shown to be contra-effective, because showing certain negative behaviour to be commonly practiced actually made it look more acceptable and resulted in more people engaging in it.

On the other hand there is the copycat effect whereby people would be encouraged to engage in certain behaviour because it is widely discussed (for example, sensational news about murder and suicide, or a novel or series/film about similar topics, resulting in people who had such tendencies imitating the said behaviours). It has been suggested that the way these topics are viewed could prevent people from engaging it the said behaviour (for example, emphasizing the grief of the victims’ relatives).

So does the way certain popular (widely practiced or widely discussed) negative behaviour is viewed actually effect whether or not it will be imitated by those who are prone to that behaviour (the first case suggests that it doesn't, the second case suggests that it does)? Or otherwise, in what way are those two effects different so that no contradiction arises?

(I’m sorry for the lack of references; I read about these topics a long time ago and I’m not sure I can find the sources.)

$\begingroup$Welcome to psych.SE. This question may be a bit broad for this forum, given the number of possible behaviors to consider, and the numerous ways they may be presented or discussed... Perhaps you can narrow the question down to a single behavior and presentation pair? I suspect that a lot of variables may be at play here.$\endgroup$
– Arnon Weinberg♦Nov 10 '18 at 0:40